Method of pumping concrete containing porous aggregates



United States Patent Ser. No. 201,239

5 Claims. (Cl. 259-447) This invention which is a continuation ofapplication Serial No. 777,608 filed December 2, 1958, and nowabandoned, relates to pumping concrete containing porous lightweightaggregates and more particularly comprises a new and improved method fortreating the aggregate to make it readily pumpable.

Great difiiculty has been encountered in connection with pumpingconcrete containing porous lightweight aggregates made of expanded claysand shales, natural materails such as pumice, or by-products such ascinders and blastfurnace slag. Mixes which contain these materials,although plastic and mobile enough at atmospheric pressures, oifer greatresistance to pumping when heads of as little as 60 p.s.i. oppose theirflow. It has also been found that when concrete mixes containing porouslightweight aggregates are subjected to high pressures for any purpose,they do not develop their expected compressive strengths when allowed toset. Some of these difficulties have severely limited the utility oflightweight concrete, particularly in the building of tall structures.Serious studies of these problems as discussed on page 77 of PumpcretePractice (1955 edition), published by Chain Belt Company of Milwaukee,Wisconsin have heretofore failed to ofier a suitable solution.

The primary object of my invention is to provide a method forpretreating lightwelht 11:. s so as to make the con aimng the aggregatereadily staph. under ressure and umpable...

Another ob ect of my invention is to avoid the harmful effectsordinarily encountered in the end product when concrete mixes containinglightweight aggregate are subjected to pressures appreciably aboveatmospheric conditions.

To accomplish these and other objects, my invention includes a methodfor pretreatin the aggre ates so that they are substantially incapa bleof t bsgr bgrg mix ggwatgr; and cehre'fit'paste'T/itli which they arecombined in the mantra Tests have revealed that the difiicultiesdeveloped in pumping the concretes containing the lightweight porousaggregates have resulted directly from the ability of the aggregate toabsorb cement paste and mixing water.

The internal voids in the porous lightweight gggneggtg, which normallycon am gases are rst evacuated in a closed system and thereafter the evt with an incompressible uid as water, The water introduced mm the voidsprevents the cement paste and mixing water from later entering the voidswhen the aggregate is combined with the other materials which make upthe concrete mix. The water initially introduced into the voids in theaggregate enhances the end product for when the mix is later poured thewater in the voids evaporates slowly and insures slow drying from theinside to the surface. Moreover, when the aggregate is treated asdescribed, any mix mobile at atmospheric pressure remains equally mobileunder applied pressure of any practical magnitude.

These and other objects and features of my invention will be betterunderstood and appreciated from the following detailed description ofseveral embodiments thereof. In order to gain a full appreciation of theinvention, several experiments will be described below. Theseexperiments related to a typical mix of structural light- EXAMINERPatented May 19, 1964 weight concrete composed of 523 lbs. of cement,1050 lbs. of sand, 900 lbs. of porous lightweight course aggregate andan agent to entrain approximately ten percent air by volume when mixing.

Experiment 1 To determine the effects of pressure upon the lightweightaggregate concrete described above, the mix was placed in a transparentLucite cylinder having a four inch inner diameter. This mixture in thecylinder was subjected to pressure and the level of the fluids in themix dropped immediately when the pressure was applied. The mix startedto lose mobility. At 60 p.s.i., the fluids had substantially disappearedand the mix was immobile. At p.s.i., there were no fluids apparent, andthe mix acquired the appearance of point contact concrete. The coarseaggregate did not move when the vessel was inverted.

When the pressure was released from the cylinder, the fluids reappeared.Some segregation occurred and a frothy material rose to the surface ofthe mix. Thereafter, when the mix was allowed to set and dry, it failedto develop any appreciable compressive strength although the mix wasdesigned to obtain a compressive strength of at least 2,500 lbs. persquare inch.

The experiment indicated that the fluids in the mix were driven into theinterior and surface voids of the aggregate as the applied pressurecompressed the gases which ordinarily fill the voids under atmosphericconditions. The failure of the material to deveolp the expectedcompressive strength indicated that a substantial quantity of the cementpaste remained in the voids after the pressure was released and as aresult, there was insuificient binder available to hold the aggregatetogether.

Experiment 2 The transparent cylinder was filled to a height of 8 /2inches with the porous lightweight course aggregate used in the abovedescribed mix. The material weighed 1125 grams loose dry. Afterweighing, the vessel was sealed and evacuated with an aspirator whichgenerated 23 inches of vacuum. Because the gases which fill the voidsare subject to the natural gas laws, it was concluded that approximatelyseventy-five percent of the gas in the voids had been evacuated. Whileunder the vacuum, water was introduced into the cylinder until itreached a level three inches above the aggregate. A moderate amount ofturbulence was noted. Thereafter, the vacuum was released.

Because only twenty-three inches of vacuum had been applied, it wasassumed that not all of the gas had been displaced by the water.Therefore, 150 lbs. per square inch of air pressure was applied to thecontents of the cylinder. Some bubbling occured and the water leveldropped approximately one inch. Thereafter, when the pressure wasreleased and applied in cycles several times, no further change in thewater level occurred.

When the material was removed from the cylinder, drained, and weighed,some fines were lost in the process but the drained weight of thematerial was 1335 grams. By accounting for the loss of fines, theexperiment indicated that 210 grams of water had displaced an equivalentvolume of gas. The material was then allowed to sit at 70 F. fortwenty-four hours. After that period, the material weighed 1302 grams,indicating that 177 grams of water remained in the aggregate.

The experiment proved that the twenty-three inches of vacuum did in factevacuate approximately seventy-five percent of the gas in the voids andthus, the gas in the voids complies with the gas laws. The gas occludedin the voids was squeezed out by the initial application of pressure anddisplaced by the water.

If lightweight aggregate is treated in this manner, it will not permitentry of either mixing water or cement paste into the aggregate voidswhen mixes of concrete containing lightweight aggregate are subjected topressure. Therefore, mixing water later mixed with the aggregate,cement, sand and other materials will provide the necessary lubricationto permit pumping of the material. Moreover, when the mixture containingthe pretreated aggregate is poured and allowed to set and dry, it willacquire its predicted compressive strength for the cement paste will notbe absorbed in the voids. Rather, it will perform its intended functionof binding the aggregate and sand. Further tests with the mix containingthe aggregate proved these conclusions valid.

Experiment 3 To determine whether the application of pressure alonewould cause the water to displace the gas in the voids, the followingexperiment was conducted. The four inch inner diameter cylinder wasfilled to a height of 8 inches with the same aggregate used inExperiments 1 and 2. As stated above, the aggregate weighed 1125 grams.Water was added to the aggregate and filled the cylinder to a heightthree inches above the level of the aggregate. The contents of thecylinder was then subjected to 150 p.s.i. of pressure. Some bubbling wasnoted and the level of the water fell approximately two inches. When thepressure was released, the level of the water rose about one-half inchand during several additional cycles of pressure and relief, the waterlevel dropped approximately one-half inch and recovered the same amount.

After this treatment, the material was drained and weighed. The drainedweight of the material was 1285 grams, an increase of 160 grams over theloose dry weight. After the material sat for twenty-four hours in 70 F.air, the material weighed 1224 grams, indicating that 99 grams of waterremained in the voids.

The experiment indicated that approximately seventyfive percent of thegas remaining in the surface saturated material was displaced by thefirst application of pressure as shown by the initial drop in the waterlevel of two inches followed by the recovery of one-half inch. Theremaining twenty-five percent of the occluded gas would not be displacedby the application of 150 psi. as shown by the repeated drop in waterlevel of one-half inch when pressure was reapplied and the subsequentrecovery of the water level when pressure was released.

Experiment 4 To determine the relative quantities of water absorbed inthe voids of the aggregate as compared to the water which would beabsorbed at atmospheric pressure, an 8 /2 inch column of the aggregatewas placed in the cylinder and weighed 1125 grams, as in the previousexperiments. The aggregate was submerged in water in the cylinder fortwenty-four hours and thereafter drained and weighed. After thistreatment, the material weighed 1255 grams indicating that approximately130 grams of water had been absorbed. It is apparent from thisexperiment that approximately one-half of the voids in the aggregate areunaffected by even the most thorough saturation and the gas remaining inthe voids is more than sufiicient to impair efforts to pump any mixcontaining a substantial volume of porous aggregate and to makeproblematical the quality of any concrete subjected to the pressuresencountered in pumping.

Additional tests have revealed that the water which fills the interiorvoids is not readily available to the cement paste while it is gellingand does not, therefore, impair the quality of the concrete. Theconcrete dies slowly as water evaporates from the mass giving theconcrete a highly beneficial slow moist cure from the inside out. Itwill also be recognized that if hot water is used to fill the interiorvoids of the aggregate and the pretreatment 4 occurs immediately beforemixing, the heat is available to cause the cement paste to gell morequickly. This, of course, is an added benefit derived from the process.Moreover, if the water contained in the voids is frozen, it will have noeffect on the concrete other than to retard drying.

Although the foregoing description has suggested that the interior voidsof the aggregate should be filled with Water, it is to be understoodthat other substantially noncompressible fluids may be employed so longas those used are compatible with the concrete chemistry. It is onlynecessary that the interior voids be filled with a fluid which preventsthe mixing water and paste from entering them. The mixing waterordinarily used in the mixture will saturate the surface of theaggregate and make possible the maintenance of mobility necessary topumping. The substantially incompressible fiuid prevents the cementpaste and mixing water from entering the interior voids while the mixingwater saturates the surfaces and prevents the surface voids fromabsorbing any appreciable quantity of the paste. When the porousaggregate is treated in this manner, any mix mobile at atmosphericpressure is equally mobile under applied pressures of any practicalmagnitude. It should also be appreciated that the pretreatment of theaggregate is useful in preparing mixes containing porous materials forextrusion because the mix will not change its character under pressure.A change of character is impossible in view of the manner in which theaggregates have been treated.

In addition to making the ultimate mixture pumpable, the process hasother applications. For example, a system has been developed for fillingforms with aggregate and then filling them with grout. Some difiicultyhas been encountered due to the failure of the grout completely to fillthe voids around and between the aggregate particles. If the mass isfirst evacuated, no voids can develop in the mass. The grout completelyfills the voids as is desired. It will also be recognized that thisprocess may be applied to precast concrete members and offers a means ofachieving the most dense possible concrete with the maximum aggregatecontent.

In the foregoing description, I have described in detail my invention ofpretreating the aggregates used in concrete. In the preferred method ofmy invention, the interior voids of the aggregate are first evacuated ina closed system and thereafter, water is introduced to the aggregatewhile the vacuum is maintained. Subsequently, pressure is applied to themixture if necessary or desirable. The necessity for the application ofadditional pressure normally will be determined by the magnitude of thevacuum initially applied. As indicated in the experiments, whentwenty-three inches of vacuum are generated, approximately seventy-fivepercent of the gas in the voids is evacuated. Thus, to fill the voids,it is necessary to subject the mixture to a considerable pressure. Ofcourse, the head to be encountered by the particular mix when laterpumped or subjected to other treatment will determine the necessaryamount of displacement of the gas by the incompressible fluid. When thehead to be encountered is not appreciably above atmospheric pressures,it is possible to avoid the evacuation step and employ the treatmentdescribed in Experiment 3. It will be recalled that following thatprocedure, approximately seventy-five percent of the gases in the voidswere dis placed by water.

It will also be appreciated that the method employed by applicant forpretreating the aggregate does not require unusual equipment. Rather,the equipment necessary to evacuate any chamber containing the aggregateand the equipment necessary to apply the necessary pressures to it maybe built economically and are not of the type which are costly tooperate.

The invention also contemplates a method of pumping concrete containingporous aggregates in which the in terior voids are filled with anincompressible fluid as water without the need of using pressures aboveatmospheric pressures. In this embodiment dry or substantially dryaggregates are subjected to a high vacuum preferably at leastapproximately a thirty inch mercury vacuum. Lesser vacuums are possiblebut inferior results will be obtained. Vacuums below a twenty-three inchmercury vacuum are relatively ineffective. While under the vacuum anincompressible fluid as water is mixed with the aggregates and thevacuum is thereafter reduced preferably to atmospheric pressure, nopressure above atmospheric need be applied. This process replaces thegases in the interior voids with the fluid to make the aggregates stableand pumpable. The treated aggregates may thereafter be combined andmixed with sand, cement and mixing water and subjected to a pressurehead for propelling the mix. Here too the fluid may be heated above roomtemperature for improved drying results. This method is adapted for acontinuous process rather than a batch process.

Having described my invention, I claim:

1. A method of pumping concrete containing a porous lightweightaggregate comprising the steps of subjecting the aggregate to a vacuumthereby evacuating the interior voids of the aggregates,

mixing water ,with the aggregate while maintaining the vacuum,

next subjecting the mixture of water and aggregate to pressure aboveatmospheric pressure to replace the gases evacuated from the voids withwater,

and thereafter combining and mixing the aggregate with sand, cement andmixing water and next applying a pressure head to propel the mix. 2. Amethod as set forth in claim 1 wherein an air entraining agent is addedto the aggregate with said sand, cement and mixing water.

3. A method of pumping concrete containing a porous lightweightaggregate having interior voids comprising the steps of mixing anincompressible fluid with said aggregate,

subjecting the aggregate and fluid to a vacuum whereby gases in theinterior voids of said aggregates are evacuated and said gases arereplaced with said fluid,

and thereafter combining and mixing said aggregate with sand, cement andmixing water and then applying a pressure head to propel the mix.

4. A method as set forth in claim 3 wherein said vacuum comprises atleast substantially a twenty-three inch mercury vacuum.

5. A method as set forth in claim 3 wherein said fluid is heated aboveroom temperature before mixing with said aggregates.

References Cited in the file of this patent UNITED STATES PATENTS886,768 De Bogory May 5, 1908 2,167,156 Morrissey et al. July 25, 19392,557,386 Lonier June 19, 1951 2,593,492 Scripture Apr. 22, 19522,921,862 Sucetti Jan. 19, 1960 FOREIGN PATENTS 7,096 Great Britain 1900

3. A METHOD OF PUMPING CONCRETE CONTAINING A POROUS LIGHTWEIGHTAGGREGATE HAVING INTERIOR VOIDS COMPRISING THE STEPS OF MIXING ANINCOMPRESSIBLE FLUID WITH SAID AGGREGATE, SUBJECTING THE AGGREAGE ANDFLUID TO A VACUUM WHEREBY GASES IN THE INTERIOR VOIDS OF SAID AGGREGATESARE EVACUATED AND SAID GASES ARE REPLACED WITH SAID FLUID, ANDTHEREAFTER COMBINING AND MIXING SAID AGGREGATE WITH SAND, CEMENT ANDMIXING WATER AND THEN APPLYING A PRESSURE HEAD TO PROPEL THE MIX.